1. Field of the Invention
This invention concerns apparatus suitable for delivery of stents to body cavities. The present invention is particularly directed to improved arrangements for releasably securing the stent to the catheter to prevent snagging of portions of the stent while the stent is being advanced through the tortuous confines of a body vessel. By way of the present invention a stent is held in place on the catheter and its ends and strut elements are kept from flaring outward by means of at least one sleeve, or sock, abutting the ends of the stent. In addition, the present invention is directed to the use of a membrane which may be disposed about a region of the stent which may be between or may overlap the portions of the stent secured by the end sleeves. Prior to stent delivery, the membrane may be retracted, may be configured so as to dissolve or otherwise degrade within the vessel, or may optionally be deployed along with the stent.
2. Description of the Related Art
Stents are tubular devices designed to maintain the patency of a bodily vessel. Stents have been used in a number of different parts of the body including the vasculature, the urinary system, the biliary ducts and the esophagus. A stent is typically delivered to a desired bodily location via a stent delivery system such as a catheter. The stent, disposed about the distal end of the catheter, is inserted in a bodily vessel and delivered to the desired bodily location where it is then deployed.
Stents may be self-expanding, mechanically expandable or hybrids. Examples of self-expanding stents include coil stents and stents made from shape memory materials such as NITINOL. One such stent is disclosed in copending, commonly assigned U.S. application Ser. No. 08/511,076. Mechanically expandable stents are most often expanded by medical balloons. Such stents are typically made of metals such as stainless steel. An example of the latter is disclosed in U.S. Pat. No. 6,033,433. Hybrid stents may be mechanically expandable in part and self-expanding in part. An example of such a stent is disclosed in copending, commonly assigned U.S. application Ser. No. 09/087,526.
Stents delivered to a restricted coronary artery, for example, may be expanded to a larger diameter by the balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer and U.S. Pat. No. 5,007,926 to Derbyshire.
Palmaz et al., 156 Radiology 73 (1985) and U.S. Pat. No. 4,733,665 describe introduction of a stent over a balloon catheter.
The stent delivery apparatus of the present invention may also utilize a self-expanding stent, which is well known in the art. A well known self-expanding stent is the woven braided stent disclosed in U.S. Pat. No. 4,655,771 (Wallsten); U.S. Pat. No. 4,954,126 (Wallsten) and U.S. Pat. No. 5,061,275 (Wallsten), although any type of self-expanding stent may be deployed using the inventive delivery system and method. The delivery system of the present invention may also be used to deliver a balloon expanded stent and may also deliver stent grafts, which are well known in the art.
As is commonly known in the art, stents may have numerous elements such as struts and other members which may flex or shift in a variety of manners during advancement of the catheter prior to stent delivery. Such flexing may result in some elements protruding outward from the catheter, which could interfere with the vessel wall or otherwise prevent further advancement of the catheter, especially in those regions of a vessel which are particularly tortuous. As a result it would be desirable to provide a covering for the stent which is extremely flexible, has a low profile and which provides sufficient coverage of the stent to prevent stent elements from protruding outward from the catheter during advancement.
The delivery systems for stents are generally comprised of catheters with the stent axially surrounding the distal end of the catheter. In many stent delivery catheters the stent is retained on the balloon catheter with a radially disposed sleeve or sheath which may be retracted or otherwise removed to release the stent. More recently stent delivery systems have included one or more stent retaining sleeves or socks disposed about the respective ends of the stent to hold the stent in the reduced configuration on the delivery catheter.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site.
Other patents which describe sleeves, and material used therefor, include Blaeser et al. U.S. Pat. No. 5,944,726 issued Aug. 31, 1999; Dusbabek et al. U.S. Pat. No. 5,968,069, issued Dec. 19, 1999; and Cornelius et al., U.S. Pat. No. 6,068,634, issued May 30, 2000, both of which are incorporated by reference in their entirety.
In addition, co-pending application Ser. Nos. 08/701,979; 08/702,149; 09/273,520; 09/549,286; 09/552,807; 09/668,496; 09/664,267; 09/664,268; all relate to stent retaining sleeves or socks.
As indicated above, in addition to employing end sleeves or socks for retaining the ends of the stent on the catheter prior to stent delivery, the present invention also employs a centrally disposed sheath which may be retracted off of the stent prior to delivery or which may be expanded along with the stent into a body vessel as desired.
An example of a method and use of a sheath to retain a stent on a catheter is respectively disclosed in U.S. Pat. No. 5,071,407 (Termin) and U.S. Pat. No. 5,064,435 (Porter), both of which use a silicon rubber sheath to compress the stent on the catheter. A similar technique is disclosed in U.S. Pat. No. 5,026,377 (Burton) and U.S. Pat. No. 5,078,720 (Burton).
A variation on surrounding the stent with a sheath is disclosed in U.S. Pat. No. 4,732,152 (Wallsten); U.S. Pat. No. 4,848,343 (Wallsten) and U.S. Pat. No. 4,875,480 (Imbert), all of which disclose using a sleeve formed of a doubled-over section of membrane to compress and contain the stent.
U.S. Pat. No. 5,234,457 discloses using a sheath to surround a mesh stent of the type disclosed in U.S. Pat. No. 4,922,405. However, in this patent the sheath is not used to compress the stent, but is used to prevent fluid from accessing the stent. The stent is impregnated with a pure gelatin or other dissolvable material which, when cured, has sufficient strength to hold the stent in its reduced delivery configuration. Other examples of sheaths for use in retaining and delivery of a stent with a stent delivery catheter are known.
The use of a sheath in conjunction with a single end sleeve or sock is also known. Co-pending application Ser. Nos. 09/228,097 and 09/332,914 include the use of a stent retaining sock or sleeve which may be placed over the distal end of the stent and secured to the catheter. A sheath may be employed to cover the entire stent including the distal end.
One drawback of using a sheath to retain a stent on a catheter, is that the sheath must inherently be retracted or otherwise removed from the stent. Such retraction typically requires movement of the entire sheath or exterior catheter in order effect release of the stent. This can be seen in Wallsten U.S. Pat. No. 4,655,771 and Wallsten U.S. Pat. No. 4,954,126 in which tubular member 23 is moved forward from position 22 to position 30. In Termin U.S. Pat. No. 5,071,407 the sheath 32 is withdrawn proximally with respect to the stent. In Porter U.S. Pat. No. 5,064,435 the sheath 38 is withdrawn proximally with respect to the stent. Burton U.S. Pat. No. 5,026,377 also moves an outer sleeve backwards relative to the stent. In Wallsten U.S. Pat. No. 4,732,152; Wallsten U.S. Pat. No. 4,848,343, and Imbert U.S. Pat. No. 4,875,480, a hose 5 is connected to a maneuvering tube 8 which runs the length of the catheter. Finally, in Heyn, finger grip 5, connected to section 58 causes outer catheter 20 and sleeve 24 to move proximally relative to the stent.
In all of the cases discussed in the preceding paragraph, movement occurs over the entire length of the catheter between the proximal end controlled by the physician and the distal end where the stent is released. This catheter movement in the vessel creates several problems. First, catheter movement can disturb or move the introducer sheath at the wound site where the catheter is inserted into the vessel. Secondly, in tortuous anatomy the added friction caused by rubbing the outer catheter against the vessel, as well as the added friction created between the inner/outer layer interface, can make deployment difficult. The translation of control movements from the proximal to the distal end is imprecise, jerky and in some instances impossible due to the increased friction caused by tortuosity. Thirdly, it can create trauma to the endothelium over the entire length of the catheter.
Another drawback to the prior art stent delivery systems discussed above is that requiring an extra sheath layer, sleeve layer or layered catheters (Heyn) increases the profile of the catheter, which is undesirable. The Heyn device described in U.S. Pat. No. 5,201,757 has a profile of 0.12 inches (3.048 mm). A reduction in profile is considered significant to those skilled in the art.
In light of the above, it would be desirable to employ a stent covering which functions to help retain the stent on the catheter but which could optionally be left on the catheter during stent delivery so as to avoid damaging the stent or causing undesirable movement of the stent during sheath retraction. It would be desirable to provide for a covering which is flexible and which sufficiently covers a stent so as to prevent stent elements from protruding outward from the catheter and interfering with a vessel wall prior to delivery. It would also be desirable to provide a covering which does not increase the profile of the stent delivery catheter beyond its profile without the covering.
All US patents, applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.